Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, generator, gearbox, nacelle, and one or more rotor blades. The rotor blades capture kinetic energy from the wind using known airfoil principles and transmit the kinetic energy through rotational energy to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid.
To ensure that wind power remains a viable energy source, efforts have been made to increase energy outputs by modifying the size and capacity of wind turbines. One such modification has been to increase the length and surface area of the rotor blades. However, the magnitude of deflection forces and loading of a rotor blade is generally a function of blade length, along with wind speed, turbine operating states, blade stiffness, and other variables. This increased loading not only produces fatigue on the rotor blades and other wind turbine components but may also increase the risk of a sudden catastrophic failure of the rotor blades, for example, when excess loading causes deflection of a blade resulting in a tower strike.
To increase the effective length of a rotor blade without increasing the likelihood of a tower strike occurring, root extenders have been developed that include an angled surface at the interface defined between the root extender and the rotor blade, thereby allowing the blade to be angled away from the wind turbine tower. For example, FIG. 1 illustrates a partial, side view of a wind turbine 10 having a conventional root extender 12 installed between a hub 14 and a rotor blade 16 of the wind turbine 10. As shown, the root extender 12 generally extends between a first end 18 and a second end 20. The first end 18 of the root extender 12 is coupled to the hub 14 via a pitch bearing 22. As is generally understood, a pitch drive 24 may be housed within the hub 14 and may be configured to engage the pitch bearing 22, thereby allowing the rotor blade 16 (and the root extender 12) to be rotated relative to the hub 14 about a pitch axis 26. Additionally, the second end 20 of the root extender 12 is coupled to a blade root 28 of the rotor blade 16. As shown in FIG. 1, to increase the clearance between the rotor blade 16 and a tower 30 of the wind turbine 10, the second end 20 of the root extender 12 defines a mounting surface 32 that is angled away from the tower 30. As a result, when the blade root 28 is coupled to the second end 20 of the root extender 12, the rotor blade 16 extends lengthwise generally perpendicular to the angled mounting surface 32, thereby angling the rotor blade 16 away from the tower 30.
However, by utilizing such a conventional root extender 12, a center of gravity 34 of the rotor blade 16 is shifted away from the pitch axis 26. Specifically, as shown in FIG. 1, while the root extender 12 provides a means for angling the rotor blade 16 away from the tower 30, it also results in the center of gravity 34 of the rotor blade 16 being offset from the pitch axis 26 by a displacement distance 36. Such displacement of the center of gravity 34 typically results in increased loads on the pitch drive(s) 24 and/or pitch bearing(s) 22 of the wind turbine 10, which can lead to decreased pitching capabilities and/or damage to various components of the wind turbine.
Accordingly, a root extender and/or a rotor blade configuration that allows a rotor blade to be angled away from a wind turbine tower without shifting the blade's center of gravity away from the pitch axis would be welcomed in the technology.